How to fix the Android AdMob "Unable to obtain a JavascriptEngine" error?

Question

MainActivity

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {

        MobileAds.initialize(this) {}
        MobileAds.setRequestConfiguration(
            RequestConfiguration.Builder()
                .setTestDeviceIds(listOf("ABCDEF012345"))
                .build()
        )

        val adRequest = AdRequest.Builder().build()
        Log.d("Activity", "Is Test Device? : ${adRequest.isTestDevice(this)}")
        adView.loadAd(adRequest)

        adView.adListener = object : AdListener() {
            override fun onAdLoaded() {
                super.onAdLoaded()
                Log.d("Activity", "@@ onAdLoaded()")
            }

            override fun onAdFailedToLoad(err: LoadAdError?) {
                super.onAdFailedToLoad(err)
                Log.d("Activity", "@@ onAdFailedToLoad()\n$err")
            }

            override fun onAdOpened() {
                super.onAdOpened()
                Log.d("Activity", "@@ onAdOpened()")
            }

            override fun onAdClicked() {
                super.onAdClicked()
                Log.d("Activity", "@@ onAdClicked()")
            }

            override fun onAdLeftApplication() {
                super.onAdLeftApplication()
                Log.d("Activity", "@@ onAdLeftApplication()")
            }

            override fun onAdClosed() {
                super.onAdClosed()
                Log.d("Activity", "@@ onAdClosed()")
            }
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout                       
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:ads="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.google.android.gms.ads.AdView
        android:id="@+id/adView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        ads:adSize="BANNER"
        ads:adUnitId="@string/banner_ad_unit_id_for_test" />

</LinearLayout>

string.xml

<resources>
    <string name="admob_app_id">ca-app-pub-000000000000~00000000000</string>
    <string name="bannera_ad_unit_id_for_test">ca-app-pub-3940256099942544/6300978111</string>
</resources>
    

I created <meta-dat> in the manifest and added admob_app_id as the android:value value inside. In the AVD test device provided by Android Studio, a test advertisement appeared without any problems, but the test advertisement did not appear on the actual device. So, as in the MainActivity code above, I called RequestConfiguration and added my mobile device ID("ABCDEF012345") to the test device ID, but the problem was not resolved. The contents of the error were as follows.

Answer 1

Probably not the solution for everyone, but fixed it for me: don't forget to turn off all kinds of adblockers.

I had a adblocker DNS configured, took me some time to finally figure that out.